Thermal Flow Meter

ABSTRACT

A thermal-type flowmeter includes a chip package. The chip package is formed through encapsulation with a resin of a sensor element, a drive circuit, a metal lead frame adapted to have mounted thereon the sensor element and the drive circuit, and a temperature detecting element. The chip package has an exposed structure in which a surface of the sensor element having the diaphragm is exposed. The temperature detecting element is mounted on the lead frame via an electrically conductive member.

CROSS REFERENCE

This application is a continuation of U.S. application Ser. No.14/363,002, filed Jun. 5, 2014, which is a National Stage application ofPCT International Application No. PCT/JP2012/079887, filed Nov. 19,2012, which claims priority to Japanese Patent Application No.2011-267451, filed Dec. 7, 2011, the disclosures of which are expresslyincorporated by reference herein.

TECHNICAL FIELD

The invention relates to a thermal-type air flowmeter having anexothermic resistor provided in a fluid under measurement, for use inmeasurement of a flow rate, and in particular, to an air flowmetersuitable for use in measurement of an intake air flow-rate as well as anexhaust gas flow-rate of the internal combustion engine of anautomobile.

BACKGROUND ART

A thermal-type air flowmeter capable of directly measuring a massflow-rate, serving as an air flowmeter that detects an intake airflow-rate of the internal combustion engines of an automobile, and soforth, is in the mainstream.

A proposal has lately been made to manufacture a sensor element of athermal-type flowmeter on a semiconductor substrate of silicon (Si), andso forth, by making use of a micro-machine technology. With this sensorelement of a semiconductor type, a cavity is formed by removing a partof semiconductor substrate, rectangular in shape, and an exothermicresistor is formed on an electrically insulating film several μm inthickness, formed on the cavity, that is, a thin-film part. Further, atemperature sensor (a temperature sensing resistor) is formed upstream,and downstream, respectively, in the vicinity of the exothermicresistor, and discrimination between down-flow and back-flow is possibleaccording to a temperature differential method whereby a flow rate isdetected on the basis of a difference in temperature between upstreamand downstream, respectively, of the exothermic resistor. The exothermicresistor is as microscopic as several hundred μm in size, and can beformed in the shape of a thin film, so that the exothermic resistor issmall in thermal capacity, thereby enabling faster response, and lowerpower consumption to be attained.

In Patent Document 1, there is described a mount structure for a sensorelement, and drive circuits, in the thermal-type flowmeter having thesensor element of the semiconductor type, formation of the so-calledchip-package.

In Patent Document 1, there is disclosed a configuration whereby asensor chip that detects a flow-rate of a liquid, a lead as an externalconnection terminal electrically coupled to the sensor chip, and aconnection between the sensor chip and the lead are coated, providedwith an encapsulation resin integrally disposed so as to enable aflow-rate detection part to be exposed. Further, in FIG. 2 of PatentDocument 1, there is shown an example in which a drive chip as well ismounted on a metal lead frame concurrently with the sensor chip.

CITATION LIST Patent Literature

Patent Document 1:

JP Patent Publication (Kokai) No. 2008-175780 A

SUMMARY OF INVENTION Technical Problem

With an air flowmeter having a presently operational sensor element of asemiconductor type, one with a configuration where a sensor element anddrive circuits are mounted on a ceramic substrate, such as LTCC (LowTemperature Co-fired Ceramics) and so forth, and the substrate ismounted inside a product body is in the mainstream. For the drivecircuits, use is made of LSI built in one chip by use of asemiconductor-integration technology from the viewpoint of mountability.Further, in order to protect the drive circuits from noise due todisturbance such as a surge, electromagnetic interference, and so forth,a chip capacitor is separately provided on the ceramic substrate to beelectrically coupled to the drive circuits. This chip capacitor thatprotects the drive circuits from the noise is large in capacity, beingoften disposed externally on the ceramic substrate without beingdisposed within LSI.

On the other hand, with a thermal-type air flowmeter for use in theautomobile, those including an air-temperature detection-element thatdetects the temperature of an air taken into an engine, formedintegrally therewith, account for the vast majority thereof. Thisdetection of the air-temperature is imported into an engine control unitindependently of measurement of an air flow-rate, for use in control ofcombustion inside the engine. The detection is vitally needed for thecontrol of combustion inside the engine at transient times for thepurposes such as early activation of a catalyst at the time of a coldstart, reduction in NO_(x) included in an exhaust gas emitted at a timeof a sudden change in an engine state, occurring after an enginewarm-up, and so forth. Even from these application purposes, fastresponsiveness is required of the temperature detection-element.

There are available a plurality of means that detect temperature, and inmany cases, a thermistor element is used in view of these requirements,an element called an axial-lead type, in particular, where lead wiresare arranged such that the positive pole and the negative pole are linedup substantially on the same straight line in the axial direction, beingin widespread use. The temperature detection element of the axial-leadtype is connected to a lead terminal inserted in a resin enclosure ofthe air flowmeter, by welding to be fixed thereto.

As described above, the chip capacitor configuring a protection circuitthat protects the drive circuits, and the element that detects theintake air are each individually mounted, so that a construction becomescomplicated.

It is therefore an object of the invention to provide a thermal-typeflowmeter highly accurate, with high reliability, and simple inconstruction, while being available at a lower price.

Solution to Problem

To that end, in accordance with one aspect of the invention, there isprovided a thermal-type flowmeter including a sub-path that takes in afluid under measurement, a sensor element that measures a flow-rate ofthe fluid under measurement in the sub-path, a temperature detectionelement that detects a temperature of the fluid under measurement, adrive circuit that controls a heating temperature of the sensor element,and a protection circuit that protects the drive circuit from noise,while a cavity is formed on a substrate of the sensor element, anexothermic resistor is provided on a thin-film part through theintermediary of an electrically insulating film, and a flow rate isdetected on the basis of temperature distribution in the thin-film part.Further, the sensor element and the drive circuit are mounted on a metallead fame, the entire periphery of the sensor element, the drivecircuit, and the lead fame is encapsulated with a thermosetting resin tothereby complete a chip package, and at least one of a chip componentthat protects the drive circuit, and an air-temperature detectingelement is consolidated inside the chip package.

Advantageous Effects of Invention

Thus, the invention can provide a thermal-type flowmeter highlyaccurate, with high reliability, and simple in construction, while beingavailable at a lower price.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is view showing a planar configuration of a chip packageaccording to a first embodiment of the invention;

FIG. 2 is a sectional view showing the chip package according to thefirst embodiment of the invention;

FIG. 3 is a sectional view showing a chip package according to a secondembodiment of the invention;

FIG. 4 is a configuration diagram of a thermal-type flowmeter where thechip package according to the second embodiment of the invention ismounted;

FIG. 5 is a view showing a planar configuration of the chip packageaccording to the second embodiment of the invention;

FIG. 6 is a view showing a planar configuration of a chip packageaccording to a third embodiment of the invention;

FIG. 7 is a configuration diagram of a thermal-type flowmeter where thechip package according to the third embodiment of the invention ismounted;

FIG. 8 is a view showing a planar configuration of a chip packagesimilar to that of the third embodiment of the invention.

FIG. 9 is a block diagram of a thermal-type flowmeter where the chippackage similar to that of the third embodiment of the invention ismounted; and

FIG. 10 is a sectional view of a suitable chip package based on thesecond embodiment of the invention.

DESCRIPTION OF EMBODIMENTS

Embodiments of the invention are described hereinafter.

FIGS. 1, 2 each show a configuration of a first embodiment of a chippackage according to the invention. In FIG. 1, with a chip package 1, asensor element 2, drive circuit 3, chip capacitors 4, and a chipthermistor 5 are directly mounted on a lead frame 6 as a metalsubstrate, and electrical coupling between the sensor element 2 and therespective drive circuit 3, and electrical coupling between therespective drive circuit 3 and the lead frame 6 are made via goldbonding wires 8 a, and gold bonding wires 8 b, respectively. The leadframe 6 with these chip components, such as the sensor element 2, thedrive circuit 3, the chip capacitors 4, and the chip thermistor 5,mounted thereon, is formed by molding to thereby seal the wholeperiphery thereof with the use of a thermosetting resin 9.

As shown in the sectional view of FIG. 2, the chip components includingthe sensor element 2, and so forth are fixedly bonded to the lead frame6 by the intermediary of respective adhesives 7 a, 7 b. As for theadhesive 7 b that is electrically conductive, for use in the chipcapacitor 4, and the chip thermistor 5 depicted in FIG. 1, inparticular, there is the need for using an electrically conductiveadhesive in order to secure conduction between an electrode of each ofthese chip components and the lead frame 6. The sensor element 2 thatmeasures a flow-rate under measurement has a cavity 10 formed in asemiconductor substrate, and a thin-film part 11 several μm in thicknessis formed therein. An exothermic resistor is formed in the thin-filmpart 11 by the intermediary of an electrically insulating film,temperature sensing resistors are formed in the vicinity of theexothermic resistor, and upon the thin-film part being heated up by theexothermic resistor, variation in temperature distribution, occurringdepending on variation in flow-rate of a fluid flowing on the surfacethereof, is detected by the temperature sensing resistors formed in thesurroundings to thereby measure a mass flow-rate. On the basis of thesemeasurement principles, the thin-film part 11 of the sensor element 2 isencapsulated with a resin in such a way as to be partially exposed outof the thermosetting resin 9 covering the periphery thereof.

Further, aluminum electrodes are formed on the outer peripheries of thesensor element 2 and the drive circuit 3, respectively, the sensorelement 2 is connected to the respective drive circuit 3 through directcoupling between the aluminum electrodes via the gold bonding wires 8 a,and furthermore, the lead frame 6 is connected to the power supply aswell as the GND of a drive circuit, other than the aluminum electrodesof the respective drive circuit 3, or output aluminum electrodes, viathe gold bonding wires 8 b. In the respective drive circuit 3, a signalthat controls a temperature of the exothermic resistor formed in thesensor element 2, and a signal detected by the sensor element 2 areconverted into a signal indicating an equivalent flow-rate. Theseflow-rate signals are each imported and fetched from the respectivedrive circuit 3 through respective input-output terminals 12 protrudingout of the thermosetting resin 9 via the gold bonding wires 8 b.

In FIGS. 1, 2, a configuration is shown whereby the chip capacitors 4that protect the drive circuit 3, and the chip thermistor 5 serving asan air-temperature detection-element, are concurrently encapsulated withthe resin; however, use may be made of another configuration wherebyonly either one of those chip components is consolidated inside the chippackage 1. In this case, the thermal-type flowmeter is simplified inconfiguration, thereby enabling back-end production process steps to besimpler, so that advantageous effects of the invention can be obtained.

Now, there is described hereinafter problems with the configuration forencapsulating the sensor element of the semiconductor type, as proposedby the present invention, with the use of the resin. As described withreference to FIG. 2, the cavity 10 is formed in the sensor element 2,the cavity 10 having the thin-film part 11 several μm in thickness. Thethinness of the thin-film part 11 greatly contributes to fast response,as the feature of the thermal-type flowmeter making use of the elementof the semiconductor type. On the other hand, the thin-film part 11 issensitive to mechanical stress and stress attributable to thermalexpansion/shrinkage, owing to smallness in the thickness thereof, sothat care is required in a production process, in particular. If a metalmold for molding comes in direct contact with the thin-film part 11 atthe time of the molding with the use of the thermosetting resin 9, thiswill pose the risk of causing damage to, and a crack on the thin-filmpart 11 because of the feature described as above. Further, if thecavity 10 of the sensor element 2 is hermetically sealed with the use ofthe thermosetting resin 9, this will cause an air sealed therein torepeatedly undergo expansion/shrinkage, depending on variation inambient temperature, and so forth, whereupon stress will be applied tothe thin-film part 11 to thereby raise a concern about adverse effectsexerted on detection accuracy in flow-rate.

In order to circumvent those problems described in the foregoing, at thetime of forming the chip package proposed by the present invention bymolding, a relief (concave in shape) is preferably provided at, forexample, a spot where the metal mold for molding is apt to come incontact with the thin-film part 11 to implement the molding in such away as to prevent the metal mold from coming in direct contact with thethin-film part 11, while partially exposing the thin-film part 11 of thesensor element 2 out of the thermosetting resin 9 after the molding.Further, in connection with a problem arising at the time ofhermetically sealing the thin-film part 11 of the sensor element 2, forexample, a function for serving as a path 13 is preferably imparted inadvance to the lead frame 6 with chip components mounted thereon, asshown in the section of a chip package according to a second embodimentof the invention, shown in FIG. 3, and a part of an outlet 14 of thepath 13 is preferably pressed down with the metal mold for molding atthe time of molding to thereby allow the outlet 14 to communicate withthe outside of the chip package 1. By so doing, since the cavity 10 ofthe sensor element 2 communicates with the outside of the thermosettingresin 9 at all times, expansion/shrinkage of the air sealed in thecavity 10, attributable to variation in the ambient temperature, will beaccommodated by running out of the thermosetting resin 9 to outside andsuction thereof from outside to thereby prevent stress from beingapplied to the thin-film part 11.

A suitable layout of the chip components to be mounted in the chippackage is described hereinafter with reference to FIGS. 3 through 5.

Key points in the mounting of the chip package in the thermal-typeflowmeter are described hereinafter with reference to FIG. 4. FIG. 4shows a configuration of the thermal-type flowmeter in the case wherethe chip package, as shown in the section view of FIG. 3, is mountedtherein. The chip package is fixed to the enclosure 15 of thethermal-type flowmeter. As for a fixing method in this case, fixing ispreferably made with the use of a thermosetting adhesive that has beenused in various cases in the past. Otherwise, use of a room-temperaturesetting type adhesive, or use of a mechanical fixing means poses noproblem, in particular. A sub-path 17 that takes in an air flowinginside an intake pipe path 16 is formed at the tip of the enclosure 15.With the sub-path 17, a path is made up by a cover that is disposed insuch a way as to clamp the enclosure 15. The thin-film part 11 of thesensor element 2, exposed out of the thermosetting resin 9 of the chippackage 1, and the chip thermistor 5 that detects an air-temperature aredisposed in the enclosure 15 in such a way as to be placed inside thesub-path 17. Further, as for the shape of the sub-path 17, the sub-path17 is shown in FIG. 4 by taking the case of the sub-path 17 being astraight-line in path-shape by way of example, however, a path-shapecapable of causing the air taken into the sub-path to swivel around,such as a detour-shape, and so forth, may be adopted. Other chipcomponents, encapsulated by the resin of the chip package 1, that is,the drive circuit 3, and the chip capacitors 4 are disposed in a circuitchamber 18, and the sub-path 17 is partitioned off from a boundary 19 ofthe circuit chamber 18 by use of a means capable of keeping airtightnessbetween the sub-path 17 and the circuit chamber 18. The input-outputterminals 12 protruding out of the chip package 1 are connected toconnector terminals 21, respectively, by welding, and so forth, insidethe circuit chamber 18, and a signal is outputted from a connector 20.

FIG. 5 is a view showing a planar configuration of the chip packageshown in FIG. 3. As previously described, the sensor element 2 thatdetects the flow rate, and the respective drive circuit 3 are mounted onthe lead frame 6 to be electrical coupled with each other via the goldbonding wires 8 a. In the case of connection by bonding with the use ofthe gold bonding wires, the sensor element 2 is preferably in closeproximity to the respective drive circuit 3, so as to be away from eachother on the order of 2 to 4 mm because of constraints due to a heightas well as a length of a gold bonding wire loop. A width and a length ofthe lead frame 6 at each place where the sensor element 2 and the drivecircuit 3 are mounted are limited by a size of the sensor element 2 andthe drive circuit 3, respectively and routing of the input-outputterminal 12. In view of these circumstances, it is reasoned that thechip package 1, basically a rectangle in outer shape, and minimum insize, while matching sizes as well as dispositions of respective chipcomponents mounted therein, is optimal.

Next, respective configurations of the path linking the cavity formed inthe sensor element to the outside of the thermosetting resin, and theoutlet of the path, together with dispositions thereof, are describedhereinafter with reference to FIGS. 3 through 5. If the formation of thepath 13 shown in FIG. 3 is executed in parallel with the dispositions ofthose chip components, this will be most efficient in view of respectiveshapes of the spots of the lead frame 6, where the sensor element 2 andthe drive circuit 3 are mounted, respectively. More specifically, thepath 13 is suitably formed directly underneath the sensor element 2, andthe drive circuit 3, respectively. In this connection, if the outlet 14of the path 13 is provided between the sensor element 2 and the drivecircuit 3, this will cause intermingling with the respective goldbonding wires 8 a, and therefore, the formation of the path 13 ispractically impossible. Accordingly, the outlet 14 is preferablyprovided at a location on a side of the drive circuit 3, directlyopposite from the disposition of the sensor element 2, as shown in FIG.5. For these reasons, if the sensor element 2, the drive circuit 3, thecavity 10 of the sensor element 2, and the outlet 14 communicating withthe outside of the thermosetting resin 9 are disposed in the samestraight-line direction, and the drive circuit 3 is disposed between thesensor element 2 and the outlet 14, this will enable the chip componentsto be efficiently disposed to thereby reduce the size of the chippackage 1.

As shown in the planar configuration of the chip package according tothe embodiment of the invention, shown in FIGS. 1, and 5, respectively,the shape of the thermosetting resin 9 covering the lead frame 6 withthe chip components mounted thereon is the rectangular chip package 1,symmetrical about the midpoint thereof, as seen in the front elevationof the chip package 1. In the case of this configuration, since thewhole periphery of the chip thermistor 5 that detects theair-temperature is encapsulated with the thermosetting resin 9, as isthe case with the other chip components, the chip thermistor 5 small inthermal capacity undergoes a pseudo-increase in thermal capacity, sothat there is the risk of deterioration in trackability, that is,responsiveness against variation in the air-temperature. Furthermore,there is a concern about a possibility of deterioration in detectionaccuracy with respect to the temperature of the fluid under measurement,owing to heat transfer occurring via the intake-pipe path, and theenclosure 15 of the thermal-type flowmeter by the intermediary of thethermosetting resin 9 sealing the whole periphery, and the lead frame 6.This problem can be overcome by the following countermeasures.

Next, a preferable disposition of the chip thermistor 5 that detects thetemperature of the fluid under measurement, and a chip package structureare described hereinafter with reference to FIGS. 6 and 7. FIG. 6 is aview showing a planar configuration of a third embodiment of a chippackage according to the invention. In order to overcome the problemdescribed as above, a lead frame 6 on which a chip thermistor 5 is to bemounted is preferably extended before the chip thermistor 5 is mountthereon, and a shape of the resin 9 for encapsulation, as well, ispreferably in an irregular shape with only a part thereof, correspondingto a part of the lead frame 6, where the chip thermistor 5 is mountedthereon, being protruded. By so doing, it is possible to check thepseudo-increase in the thermal capacity, and adverse effects on thedetection accuracy owing to the heat transfer from the thermosettingresin 9 and the lead frame 6, respectively.

FIG. 7 shows an example in which the chip package according to the thirdembodiment of the invention is mounted in the thermal-type flowmeter. Asa preferable method for mounting the chip package 1 in the enclosure 15,it is suitable to dispose the chip thermistor 5 upstream in the flow ofan intake air, in the case where the chip thermistor 5 is mounted in theenclosure 15 of the thermal-type flowmeter, that is, at a location wherean air comes in direct collision therewith. Disposition of the chipthermistor 5 at the location where the air comes in direct collisiontherewith will enable variation in the air-temperature to be detectedfaster with higher accuracy. In FIG. 4, both a flow-rate detector 11 ofthe sensor element 2, and the chip thermistor 5 are disposed inside thesame sub-path 17. As for the sub-path 17, various shapes, such as thedetour-shape, and so forth, can be taken into consideration, and in thecase where the chip package depicted in FIG. 6 is applied to thesub-path 17, it is preferable to dispose the sensor element 2 in thesub-path 17, whereas the chip thermistor 5 is disposed directly in theintake-pipe path 16. By so doing, the air-temperature can be detected bythe chip thermistor 5 with high accuracy without depending on the shapeof the sub-path 17.

Now, a variation to the third embodiment of the invention is describedwith reference to FIGS. 8, and 9. FIG. 8 is a view showing a planarconfiguration of the variation to the third embodiment of a chip packageaccording to the invention. The configuration has a feature in that thechip thermistor 5 is disposed at a position directly opposite from adirection in which the input-output terminals 12 protruding from thethermosetting resin 9 of the chip package 1 is protruded, that is, at aposition on a side of the chip package 1, adjacent to the tip thereof.In this configuration as well, a part of the lead frame 6, with the chipthermistor 5 mounted thereon, is extended, and the thermosetting resin 9as well is in a shape where only a part thereof, corresponding to thepart of the lead frame 6, with the chip thermistor 5 mounted thereon, isprotruded, so that advantageous effects owing to the configurationdescribed with reference to FIG. 7 can be similarly obtained. Further,FIG. 9 shows an example of a configuration in the case where the chippackage according to the variation is mounted in the thermal-typeflowmeter, and if the sub-path 17 is in the shape of a straight-line,the sensor element 2 is preferably disposed in the sub-path 17, and thepart of the lead frame 6, for mounting the chip thermistor 5, protrudedon the tip side of the enclosure 15, is preferably disposed in theintake-pipe path 16.

There is described hereinafter a suitable embodiment of a chip packageaccording to the invention, in respect to the thickness thereof, bycomparing FIG. 3 with FIG. 10. First, T1 denoted in FIG. 3 is thethickness of the chip package according to the second embodiment of theinvention. Assuming that the chip package is mounted in the thermal-typeflowmeter, in the case of the chip package proposed by the invention, ingeneral, an upper limit of the thickness of the chip package isdetermined depending on the width of the enclosure and flexibility inmounting. If the thickness is excessively small, rebounding willobviously occur due to insufficiency in strength, and so forth, andtherefore, a lower limit value as well exists, however, there isbasically the need for holding back the thickness of the chip package asmuch as possible from the standpoint of layout flexibility.

To describe further by taking an example shown in FIG. 3, the respectiveloop heights of the gold bonding wires 8 a, 8 b can be cited as one offactors for determining the thickness of the chip package. Therespective loop heights of the gold bonding wires 8 a, 8 b are dependenton a chip height of the sensor element 2 as well as the drive circuit 3,as respective targets for connection, and a step (a distance from thesurface of each of the chip components to a chip-component mountingplane) in the lead frame 6. In other words, if the sensor element 2differing in chip height from the drive circuit 3, and the drive circuit3 are adopted, this will be more advantageous from a standpoint ofreducing the thickness of the chip package 1.

FIG. 10 shows an example in which the drive circuit 3 is lower in heightthan the sensor element 2. If such a combination of the chip componentsis adopted, a reduced portion of the height can be assigned for use asthe respective loop heights of the gold bonding wires 8 a, 8 b, so thatthe highest point of the gold bonding wires 8 a as well as the highestpoint of the gold bonding wires 8 b can be lowered, thereby enabling thethickness of the chip package 1 to be smaller (T1>T2). Further, inconnection with a relationship between the sensor element 2 and thedrive circuit 3, in respect of the chip height, if a combination of thesensor element 2 lower in the chip height than the drive circuit 3, andthe drive circuit 3 are adopted, similar advantageous effects can beobtained, so that adoption of such a combination of the chip componentsposes no problem in particular.

LIST OF REFERENCE SIGNS

-   1 chip package-   2 sensor element-   3 drive circuit-   4 chip capacitor (protection circuit)-   5 chip thermistor (air-temperature detecting element)-   6 lead frame-   7 a adhesive-   7 b electrically conductive adhesive-   8 a, 8 b gold bonding wire-   9 thermosetting resin (encapsulation resin)-   10 cavity-   11 thin-film part (flow-rate detector)-   12 input-output terminal-   13 path-   14 outlet-   15 enclosure-   16 intake pipe path-   17 sub-path-   18 circuit chamber-   19 boundary-   20 connector-   21 connector terminal

1. A thermal-type flowmeter including a sensor element having anexothermic resistor formed on a diaphragm, a temperature detectingelement, and a drive circuit electrically connected to the sensorelement, comprising: a chip package formed through encapsulation with aresin of the sensor element, the drive circuit, a metal lead frameadapted to have mounted thereon the sensor element and the drivecircuit, and the temperature detecting element, wherein: the chippackage has an exposed structure in which a surface of the sensorelement having the diaphragm is exposed, and the temperature detectingelement is mounted on the lead frame via an electrically conductivemember.
 2. The thermal-type flowmeter according to claim 1, wherein thechip package is in a shape with a portion thereof, where the temperaturedetecting element is mounted, being protruded.
 3. The thermal-typeflowmeter according to claim 1, further comprising a sub-flow path thattakes in a part of a fluid under measurement passing through a main flowpath, wherein the chip package is provided such that a portion on whichthe sensor element is mounted is disposed in the sub-flow path and aportion on which the temperature detecting element is mounted isdisposed in the main flow path.
 4. The thermal-type flowmeter accordingto claim 2, wherein a direction of the protrusion of the portion of thechip package is an upstream direction of a flow of the fluid undermeasurement.
 5. The thermal-type flowmeter according to claim 2, whereina direction of the protrusion of the portion of the chip package is adirection perpendicular to the flow of the fluid under measurement. 6.The thermal-type flowmeter according to claim 2, wherein the chippackage has a connection terminal for electrical connection with anoutside of the chip package, and is in a shape with the portion thereofbeing protruded in a direction perpendicular to a direction of theconnection terminal.
 7. The thermal-type flowmeter according to claim 2,wherein the chip package has the connection terminal for electricalconnection with the outside of the chip package, and is in a shape withthe portion thereof being protruded in a direction horizontal to thedirection of the connection terminal.
 8. The thermal-type flowmeteraccording to claim 1, wherein: the metal lead frame has a mountingportion on which the drive circuit is mounted and a protruding portionthat protrudes from the mounting portion, and the temperature detectingelement is mounted on the protruding portion.
 9. The thermal-typeflowmeter according to claim 1, wherein the chip package has a capacitormounted on the lead frame, the capacitor being encapsulated with theresin.